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Resident killer whale feeding habits: Assessment methods, winter diet, and chum stock ID John Ford Pacific Biological Station Fisheries and Oceans Canada.

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Presentation on theme: "Resident killer whale feeding habits: Assessment methods, winter diet, and chum stock ID John Ford Pacific Biological Station Fisheries and Oceans Canada."— Presentation transcript:

1 Resident killer whale feeding habits: Assessment methods, winter diet, and chum stock ID John Ford Pacific Biological Station Fisheries and Oceans Canada Nanaimo, British Columbia

2 Methods of assessing diet in killer whales 1.Chemical tracers (fatty acids, stable isotopes, contaminants) from skin and blubber biopsies 2.Prey remains in stomachs of stranded animals 3.Direct observation at surface 4.Prey fragments (scales and tissue) recovered from predation sites 5.Fecal sampling J. Towers

3 Strengths and weaknesses of diet assessment methods 1.Chemical tracers (fatty acids, stable isotopes, contaminants) from skin and blubber biopsies

4 Strengths and weaknesses of diet assessment methods 2.Prey remains in stomachs of stranded animals

5 Strengths and weaknesses of diet assessment methods 3.Direct observation

6 Strengths and weaknesses of diet assessment methods 4.Prey fragments (scales and tissue) recovered from predation sites

7 Strengths and weaknesses of diet assessment methods 5.Fecal sampling

8 How reliable are prey fragments in diet assessment of resident killer whales? 1. Are surface-oriented prey over-represented? 2. Are large prey sizes over-represented? 3. Are fish with scales that are easily shed over-represented?

9 Focal animal and group observations and u/w video indicate salmon prey routinely brought to surface and broken up, usually for sharing Adult females shared 90% of prey, males 24%, and subadults 59% (n = 213 feeding events) 1.Are surface oriented prey over-represented?

10 Stomach contents of three stranded residents consistent with sharing of salmonids, but not necessarily other species: – A09: 19 Chinook, anterior bones only; 15 lingcod (only 2 large), mostly complete – C16: 6 Chinook, anterior bones only; 5 halibut, 18 Dover sole, apparently complete – Unknown SR female: 1 Chinook, posterior bones only 1.Are surface oriented prey over-represented?

11 Tracking studies in Johnstone Strait indicate that Chinook swim at a mean depth of 69.9 m (± SD 57.3), max 398 m Sockeye tracked in same area swam at mean depth of 14.9 m (± SD 57.3) Sockeye rarely appear in prey samples, despite being > 4 times shallower than Chinook on average 1.Are surface oriented prey over-represented? Source: Candy and Quinn Can. J. Zool.

12 Age (years) Percentage of kills Shared (n = 144) Not shared (n = 46) Mean Chinook ages: shared = 4.28 yrs (±0.07SE, n = 117) not shared = 4.27 yrs (±0.16SE, n = 32), p=0.87 Source: Ford and Ellis MEPS 316: Sharing observed in all salmonid species taken by RKW No significant difference in age distribution of shared vs non-shared 2.Are large prey sizes over-represented?

13 Both scales and tissue were collected in 50% of feeding events involving salmonids (2004–2011) Frequency distribution similar between scales only, scales & tissue, and tissue only samples 3.Are fish with scales that are easily shed over- represented? Percent

14 How reliable are prey fragments in diet assessment of resident killer whales? No evidence that frequency of salmonids in prey fragment sampling is seriously biased Prey species IDs from fecal DNA generally consistent with results of prey fragment sampling (Hanson 2011 Workshop 1) Fecal samples revealed more non-salmonids than did prey sampling, but proportions of DNA suggest minor contribution to diet (Hanson 2011 Workshop 1) Stomach contents also suggest non-salmonids may be under represented in prey fragment sampling

15 Conclusion Both prey fragment and fecal sampling equally important techniques Fragment sampling better for accurately determining proportions of salmonids in diet, rates of prey capture in foraging bouts, and identifying when and where prey are captured Fecal sampling better for determining presence of non- salmonids, identifying prey taken over periods of up to several days

16 Month Number of feeding events Salmonid species taken by month (n = 806 feeding events). Sockeye and steelhead salmon are not illustrated due to rarity. Source: Ford et al CSAS Res Doc 2009/101 What are resident killer whales eating in winter?

17 Northern residents, Dixon Entrance 22 Nov kills, all Chinook: –0.2 SOTH (L_Thompson) –1.1 Up Willamette (Sandy) –0.2 NOTH (Barriere) –0.2 ECVI (Puntledge_F) –1.2 Up Col-Su/F (Hanford Reach) Winter – Spring Predation by RKW late November

18 Northern residents, Clarence Strait, SE Alaska, 30 Nov kills, both Chinook: –R.2 Skeena Mid –?.? SOMN (Klinaklini) Winter – Spring Predation by RKW late November

19 Southern residents (K pod), Puget Sound, Nov kills, all salmon: –0.2 yr Chinook –? Yr Chinook, LWFR-F (W Chilliwack) –5 yr Chum –? Yr Chum –Unidentified salmon Winter – Spring Predation by RKW late November

20 Southern residents (J pod), Juan de Fuca Strait, 20 Nov kill, Chinook –0.2 yr LWFR-F (Harrison) Winter – Spring Predation by RKW late November

21 NRKW female A9 (post- reproductive) Carcass recovered 7 Dec 1990 (dead < 1 week) Prey remains: –18 Chinook salmon –15 Lingcod (only 2 large) –5 Greenling –8 English sole –1 Sablefish –Various small fishes, likely prey of Lingcod Winter – Spring Predation by RKW December

22 Winter – Spring Predation by RKW December Southern residents (J pod), Str of Georgia, 28 Dec 1977 –1 kill: 2.2 Chinook Southern residents (J pod), Puget Sound, 1 Dec 2004 –1 kill: 0.3 Chum

23 Winter – Spring Predation by RKW January Northern residents (I11 and I31 pods), Queen Charlotte Strait, Jan kills, all Chinook: –2 X 1.3 LWFR-Sp (Birkenhead) –2 X 0.3 ECVI (Big –3 X 0.3 – stock to be IDd Northern residents (A5 pod), Strait of Georgia, 23 Jan kills, both Chinook: –2 X 0.3 ECVI (Big

24 Winter – Spring Predation by RKW February Southern residents (L pod), Strait of Georgia, 8 Feb kill: Chinook 0.3 LWFR-F )

25 Winter – Spring Predation by RKW March Southern residents (J pod), Strait of Georgia, 11 Mar kill: Chinook 0.3 NOMA (U_Dean)

26 Winter – Spring Predation by RKW April Southern residents (J pod), Juan de Fuca Strait, 23 Apr kill: Steelhead

27 SRKW female (genetic ID) Carcass recovered 21 May 1996 (probably dead > one month) Prey remains: –1 Chinook salmon –1 Boreopacific Armhook Squid (Gonatopsis borealis) Winter – Spring Predation by RKW April

28 Winter – Spring Predation by RKW May 36 kills, May (34 NR, 4 SR) 30 Chinook, 6 unident. salmonid

29 Genetic stock identity of chum taken off northeastern Vancouver Island (PFMA 12) by NRKW,

30 Analyzed with cbayes using 14 microsatellite markers, against baseline of 104 populations

31 Genetic stock identity of chum taken off northeastern Vancouver Island (PFMA 12) by NRKW, Analyzed with cbayes using 14 microsatellite markers, against baseline of 104 populations

32 Genetic stock identity of chum taken off northeastern Vancouver Island (PFMA 12) by NRKW, Percent Jul-Sep (n = 62) Oct-Nov (n = 87)


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